As more innovative and special telephone systems and services are being offered to telephone customers, problems arise in finding economical ways of integrating the new systems and services into the existing telephone network. For example, in providing emergency telephone service, the 3-digit telepone number 911 has been designated as the public emergency number throughout the United States. When a customer dials 911, the telephone system connects the customer to a public service answering point (PSAP), which is a call terminating facility authorized to receive and respond to emergency calls for police, fire, ambulance, etc., services.
A fundamental problem with basic 911 service is that telephone office service areas do not correspond with the boundaries of municipalities (borough, town, city, county, etc.) which are the natural governmental entities for offering emergency service. A customer placing an emergency call from a station in a municipality A might be directed to a PSAP in municipality B by the serving central office. In this case, the call must be redialed by the customer using a conventional 7-digit number, or some provision must be established at the PSAP to redial or transfer the call to a PSAP serving municipality A.
This problem has been overcome by a service known as expanded 911 (E911) service in which one feature uses dedicated trunking facilities and a tandem office to route calls to the proper PSAPs. This feature is called selective routing. In E911 service, a local electronic switching office, such as an ESS No. 1, manufactured by Western Electric Company, Inc., is used as the tandem office for 911 calls to route these calls to the correct PSAP designated to serve a calling station. The correct routing is determined on the basis of the ANI (automatic number identification) number, or directory number, of a calling station generated by the serving local office. The local office, which can also be the tandem ESS office for certain stations, receives a 911 call and obtains the ANI number in a conventional manner. If the local office is an office other than the tandem office mentioned above, the office seizes a dedicated outgoing 911 trunk to the tandem office and outpulses the ANI number to the tandem office. The tandem office contains a dedicated memory which is addressed using a translation of the ANI number to determine the routing to the proper PSAP for this calling station. The tandem office routes the call via a dedicated outgoing 911 trunk to that PSAP and outpulses the ANI number to the PSAP to identify the calling station to a PSAP attendant.
The PSAP selected by the tandem office may be a primary PSAP, which means that it has been designated by the municipality to receive initially all emergency calls. An attendant at the primary PSAP may thereafter distribute the calls via the tandem office to secondary PSAPs which are authorized for administering the specific service requested by the calling customer. For example, the primary PSAP may initially receive all calls but may specifically offer only police services; individual secondary PSAPs may offer fire, ambulance, and other types of emergency services. The distribution of a call from a primary PSAP to a secondary PSAP is called selective transfer.
Although the expanded 911 system operates quite well for providing emergency services, the dedicated 911 trunks represent a substantial expense. Moreover, because of a relatively low volume of emergency traffic, these trunks are typically used at only a fraction of their capacity. A number of other practical difficulties exist with the expanded 911 systems. For example, a customer such as a child who incorrectly dials "0" for an operator rather than 911 reaches an operator who is not integrated into the E911 system. The operator must determine how to route the call by means of a manual look-up procedure. The procedure is slow and error-prone. Moreover, the selective routing memory at a tandem office represents a considerable investment which is accessible only by the tandem office. It may be desirable to provide shared access to this memory for other services.
One potential way of providing a new E911 service and overcoming the disadvantages discussed above is to use a method similar to that to be used for offering enhanced-wide-area-telephone-service (INWATS) as described in U.S. patent application Ser. No. 924,170, filed by R. P. Weber on July 13, 1978, now U.S. Pat. No. 4,191,860 of Mar. 4, 1980. The method uses a data signaling network called the CCIS (common channel interoffice signaling) system. The CCIS system interconnects telephone offices and centralized processing facilities or data bases by a data communications network primarily for the purpose of segregating telephone signaling functions from telephone voice facilities. In the enhanced INWATS method, data is stored at a centralized data base for an INWATS subscriber. The stored data includes a list of telephone numbers, each stored in conjunction with an area code or codes from which an 800-type INWATS call to the subscriber may originate. In response to receipt of an INWATS call to an 800-type INWATS number assigned to the subscriber, a telephone office having access to the CCIS system formulates and sends a data message to the data base. The message includes the INWATS number and the area code from which the call originates. At the data base, a control program searches the stored data to ascertain a telephone number designated by the subscriber to which calls from the area code in question are to be routed. The selected telephone number may depend upon various other factors, such as day of the week, time of day, etc., as well as the location of the originating station. The telephone number designated by the subscriber for the call is formulated into another data message and transmitted to the inquiring telephone office over the CCIS system; the telephone office thereafter completes the call to the telephone number in a conventional manner.
To provide E911 service, the information stored in memory in a tandem office in the conventional E911 system is stored at a centralized data base as in the enhanced INWATS system. In one embodiment, the stored information includes, for a given originating telephone office, a list of ANI line numbers in the office. A list of telephone numbers of primary and secondary PSAPs may be stored in conjunction with each ANI number. In response to a 911 call, an originating office sends a CCIS message, including the office code and ANI number of the calling station to the data base. The data base responds with an appropriate PSAP telephone number for the calling station, and the originating office then completes the call in a conventional manner.
The above method centralizes stored information for greater accessibility and eliminates the need for dedicated trunking in providing enhanced 911 service. A major problem arises, however, in that there is no convenient way to identify a calling station automatically at the PSAP. This is a serious detriment to the provision of enhanced 911 service because of the delay and error-proneness involved in having an attendant manually obtain the information, and because calling parties sometimes hang up prematurely in an emergency situation before informing an attendant of all the information necessary to provide the needed service.
The inability to identify automatically a calling station at a PSAP arises because in a nondedicated system there is no convenient way to transmit such information over the conventional network. Even if a PSAP were equipped with access to the CCIS system and the calling station identity transmitted thereby to the PSAP, there is no way for the PSAP to associate the identity with a call arriving on an incoming trunk unless all offices involved in the connection and the PSAP have CCIS capability. If all offices and PSAPs have CCIS capability, the incoming trunk to the PSAP can be provided with the calling station identity to the PSAP via the CCIS system. It is likely to be many years before all offices have CCIS capability.